The majority of microwave popcorn containers presently in use rely on steam pressure to achieve proper package expansion. These containers tend to be quite efficient from a distribution standpoint since they can be shipped and displayed on a store shelf in flattened form, thereby taking up a minimal amount of space. Various patents disclose such packaging. Examples are U.S. Pat. No. 4,571,337 to Cage, U.S. Pat. No. 4,548,826 to Watkins, U.S. Pat. No. 3,973,045 to Brandberg, and U.S. Pat. No. 3,851,574 to Katz.
Although expandable bags are cost-effective, they are not currently the most efficient for popcorn cooking. Two problems are associated with such expandable bag packaging:
(1) Proper expansion of the package is not always achieved. This reduces the space available for the popped kernels and results in a lower yield of finished product; and
(2) Heating of the product is not always sufficient. This also results in lower yields.
Problems associated with bag expansion occur for various reasons. In some packaging, venting of steam occurs prematurely. This has been found to be a problem with the bag of Cage et al., U.S. Pat. No. 4,571,337, which relies on a weakened seal area for the venting function. This weakened seal area cannot be precisely controlled due to variations in material thickness and seal strength. Other packaging, such as that disclosed by Brandberg et al. in U.S. Pat. No. 3,973,045, shows a vent which releases steam throughout the entire cooking process. This system of venting is also unreliable because of variations in the rate of steam generated during the cooking process.
An additional cause of poor bag expansion is bag geometry. Ideally, an expandable bag will retain its expanded form when the internal steam pressure declines. This usually occurs in popcorn cooking during the latter stage of the process, when fewer kernels are being popped. Current state-of-the-art packaging relies on bag geometry which allows the bag to collapse during the early stages of steam ventilation, and only retain its expanded form during the latter stage of the cooking process.
A further problem associated with current state-of-the-art popcorn packages relates to adequately heating the popping corn within the package. Such problems are due primarily to a transfer of heat from the package to the oven floor. The Borek patent, U.S. Pat. No. 4,219,573, teaches the use of a cardboard pad to solve this problem. Although this solution is only a partial one, the packaging materials expense is increased by this solution. Bohrer et al., U.S. Pat. No. 4,553,010, describes an attempted solution to the heat transfer problem through the use of a microwave-interactive material such as a metallized polyester. This type of technology could be applied to an expandable bag. However, as with other solutions, packaging costs are increased.
In addition to the problems relating to expansion of the package and heating of the product, most microwave popcorn packages lack a convenient means for opening the package. Such convenient opening means is particularly important in microwave popcorn packaging due to the possibility of burns from escaping steam as the package is opened.